26 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxxn. 



D. Outer ramus of third uropods uniarticulate Eacrangonyx, p. 29 



DD. Outer ramus of third uropods V)iarticalate NIphargus, p. 36 



CO. Inner ramus not rudimentary, one-halftothree-fourthsas long as outer, which 



is biartieulate; telson cleft to the base, or nearly so Gammarus, p. 38 



BB. Telson entire. 



C. Third uropods with rami. 



D. Third uropods uniramous; telson short and broad Crangmn/x, p. 49 



DD. Third uropods biramous. Inner ramus rudimentary, outer uniarticulate; 



last two segments of urosome coalescent Stygonectea, p. 51 



CC. Third uropods without rami Apocrangonyx, p. 53 



AAA. First antenufe without secondary flagellum; telson entire, short and broad; 

 third uropods uniramous Orchestiid/e; Ilyalella, p. 54 



Family LYSIANASSID^E. 



Onl}" two species, Pontopore'ui lioyl Smith, and I\mtoj)ore!a jillcorv Is 

 Smith, have been described as belonging to this family. 1 have not 

 had specimens of either, but will quote Professor Smith's descriptions 

 of them. 



Genus PONTOPOREIA Ki-0yer. 



KEY TO SPECIES. 



A. Antennpe not reaching to the posterior end of the abdomen; outer ramus of third 



uropods not more than twice as long as the peduncle P. hoyi, p. 26 



AA. Antenna? extending to or beyond the tip of the abdomen; outer ramus of the 

 third uropods more than twice as long as the peduncle P. filicornh, p. 28 



PONTOPOREIA HOYI Smith. 



Gammarus brenstylis Stimpsok, MSS. (female). 



Pontoporeia affinis Smith, Am. Jour. Sci., 3rd. ser., II, 1871, p. 453; Prelim. Rep. 



on Dredgings in Lake Superior, 1871, p. 1022. 

 Pontoporeia hoyi Smith, liep. U. S. Fish Com., 1872-73, (1874) p. 647, {)!. Ji, fig. 5. 



Professor Smith's description follows: 



On first examining specimens of this species, obtained in Lake Superior in 1871, I 

 regarded them as specifically identical with the Pontoporeia affinis of the Scandina- 

 vian lakes and the Baltic. A subsequent and more minute comparison has, how- 

 ever, revealed some differences, which are apparently constant. In the form and 

 proportions of the segments of the thorax and abdomen, in the size and form of the 

 eyes, in the minute details of antennulpe, antennae, and iriouth appendages, 1 can 

 detect no differences by whi(;h it would be possible to distinguish specimens taken 

 in Lake Superior from those sent from Lake Wetter, or from the beautiful figures of 

 the Scandinavian species given by Sars.« In the first pair of legs, however, the 

 propodus in the American species is proportionately a very little shorter than in the 

 European, and the palmary margin is less oblique — that is, it is not so nearly parallel 

 with the posterior margin; the posterior margin is somewhat shorter, and furnislied 

 with fewer hairs; and there are usually two small and slender spines on the palmary 

 margin near the tip of the closed dactylus, while in the European species there are 

 no real spines upon the palmary margin, but only slender setiform hairs. In both 

 the European and American species, there is a very thin and narrow lamellar edge, 



aHistoire Naturelle des Crustacea d'Eau Douce de Norvege, 1867, p. 82, pi. vii, 

 figs. 10-25; pi. VIII, figs. 1-5. 



